Structure of the NiFe₂O₄(001) surface in contact with gaseous O₂ and water vapor

Nickel ferrite, NiFe₂O₄, is a material with interesting physical properties and useful technological applications. We have used Density-functional theory with on-site Coulomb repulsion U term to study the structure, electronic properties, and energetics of the NiFe₂O₄(001) surface and its interaction with water both in the absence and in the presence of surface oxygen vacancies. In a humid environment, water adsorbs dissociatively on the surface oxygen vacancies leading to the formation of surface hydroxyls. At high temperature, water desorbs leaving a surface containing oxygen vacancies. These defects could represent useful reactive sites for various catalytic reactions.